1. Field of the Invention
The present invention relates to a communication system having the capability of selecting a communication mode from a plurality of modes so that communication is performed in the optimum mode that best matches the equipment at a party to be communicated with.
2. Description of the Related Art
An example of communication equipment of this type is a facsimile machine, in which communication is performed at a modem speed selected from available values including 14.4 kbps, 9.6 kbps, 7.2 kbps, 4.8 kbps, 2.4 kbps, etc. The modem rate is optimally selected taking into account various factors such as the capability of the modem at the party to be communicated with, the condition of the communication line evaluated by training or TCF, and the history of communication performed in the past. In recent years, techniques to achieve a higher speed of up to 28.8 kbps in data communication have been developed. However, if the communication is performed via a modem at an ultra high rate such as 28.8 kbps, 26.4 kbps, 242.2 kbps, 16.8 kbps, various problems occur as described below.
First, to achieve data transmission at an ultra high speed, it is required to select a transmission line having the capability of a high sampling rate so as to prevent signals from being distorted. To achieve this requirement, a user at a calling end has to ask an exchange operator to select a high sampling rate transmission line before starting the ultra high speed data communication, which is a tedious job.
In some cases, a call to be transmitted is tried at an ultra high speed via a rather low-seed communication line. However, signals will be distorted and thus transmission will fail. As a result, even conventional-type high-speed modems will fall back repeatedly, which results in an increase in communication time.
Furthermore, if a high sampling rate transmission line is selected according only to the convenience of the caller, then a high sampling rate transmission line is used even when the modem of a facsimile machine at a receiving end does not have the capability of ultra high speed communication. This results in a waste of resources.
Even if the modem of the equipment at the called end has the capability of ultra high speed communication, the communication via the ultra high speed modem requires a tedious procedure before starting actual communication. That is, the user has to tell an operator of the called party that he or she desires communication at an ultra high speed rate. The operate at the called party then sets the equipment in the ultra high speed communication mode. Finally, ultra high speed data communication starts.
Furthermore, if the equipment at the called end is set in an operation mode such as an automatic receiving mode, automatic FAX-TEL selection mode, or answering machine mode, and if there is no operator near the equipment, then there is a possibility that the communication in the ultra high speed mode is impossible.
Furthermore, various conditions (for example detection of a CNG signal, pressing of a starting, key, detection of a silent state, detection of a predefined DTMF, detection of a predefined hooking operation, expiration of a predefined time after the arrival of a call), that may occur in a time period from the arrival of a call until the transition to a facsimile operation, can make it impossible to perform communication in the ultra high speed mode unless an operator is present near the equipment at the called end, even if the equipment of the called party has the capability of ultra high speed communication.
In conventional techniques, when equipment operates in an automatic FAX-TEL selection mode, transition to a voice communication mode needs 2 to 5 sec after a call has arrived, which thus results in a delay in communication. Furthermore, if a facsimile machine is set in an automatic receiving mode or in the case where a CNG signal is detected, there is a possibility that transition to a telephone mode becomes impossible. Another problem is that the increase in the type of modem transmission rates results in an increase in the probability that; there is inconsistency in the modem type between calling and called ends. To achieve proper connection between modems of various new types without problems, a new communication protocol (ITU Recommendation V.8) is expected to be established.
However, even if the protocol according to the recommendation V.8 is employed, V.8-equipment will not be able to be properly connected to equipment that has no capability of V.8, although V.8-equipment can be connected satisfactorily to another V.8-equipment.
In view of the above, it is an object of the present invention to provide an improved communication equipment.
It is another object of the present invention to provide a technique by which a proper communication line having the capability of a high sampling rate can be automatically selected without assistance of an exchange operator.
It is further object of the present invention to provide a technique for avoiding a possibility that communication via an ultra high speed modem starts before acquiring a proper communication line having the capability of a high sampling rate and thus preventing unnecessary fall-back operations that would result in a delay in communication.
It is still another object of the present invention to provide a technique by which when called equipment has a modem with the capability of ultra high speed communication, ultra high speed communication can be started without assistance of an operator at a called party.
It is another object of the present invention to provide a technique by which communication via an ultra high speed modem is possible in whatever receiving operation mode equipment at a called party is set.
It is still another object of the present invention to provide a technique by which communication via an ultra high speed modem is possible regardless of various conditions (for example detection of a CNG signal, pressing of a starting key, detection of a silent state, detection of a DTMF in a predefined fashion, detection of a hooking operation in a predefined fashion, expiration of a predefined time after the arrival of a call), that may occur during a time period from the arrival of a call till the transition to a facsimile operation.
It is another object of the present invention to provide a technique by which the operation mode can be switched quickly to a voice communication mode from any modes including an automatic FAX-TEL selection mode.
It is further object of the present invention to provide a technique by which an optimum communication line having the capability of a high sampling rate can be selected taking into account the capability of equipment at a called party thereby preventing resources from being wasted.
It is another object of the present invention to provide a technique that is compatible with existing communication equipment (G3-facsimile, for example). These and other objects and features of the present invention will be more readily apparent from the following detailed description when read in connection with the accompanying drawings.